Chucks are used used to clamp various types of rotating tools, for example, drill bits, reamers, screw taps, etc. Typical chucks include a body, jaws (typically, three), nut, and outer housings, etc., and sometimes they also include a back sleeve. In addition, some chucks include bearings and bearing gaskets that are used for decreasing friction. The housing and bearing gasket are separately tightly fitted with the body. The jaws are installed in the equally divided slant holes in the body. The nut is placed around the body and its interior has threads that interact with the jaws to form a thread drive gear. The housing is jacketed over the nut (in some situations, there is also a nut sleeve jacketed over the nut). There is a key on the housing and there is a key slot corresponding to the key on the nut to enable the housing to connect through the key and nut sleeve (nut).
The outer sleeve can be manually rotated during usage to drive the nut sleeve and/or nut to cause the jaws to move forward and backwards in the slant holes of the body and to cause the jaws to open or close with respect to the rotating tool.
The jaws of this type of clamping chuck have a thread section formed by cutting along a lateral surface, and the front end of this thread section has a thread terminal end plane. When the nut is rotated in the loosening direction and the gripping jaws drive toward the back until near the extreme position, the terminal end plane of the threads of the gripping jaws rubs against and joins with the thread end of the nut, and they are pressed close to each other. Further rotation of the nut causes transitional extrusion of the two surfaces and produces very great friction. As a result, when the nut is rotated in the tightening direction in order to tighten the tool, it is necessary to first overcome this friction which makes usage inconvenient and sometimes there can even be jamming. In addition, this friction can also increase the wear of the thread and thus influence the usage lifetime of the clamping chuck.
U.S. Pat. No. 5,913,524 discloses a clamp head with a clamp mechanism stop part. As shown in FIG. 49, there is an arresting section 2′a on nut 2′ that can rotate with the nut, and this arresting section 2′a extends in the axial direction of the gripper body. When the rotation of nut 2′ in the loosening direction causes gripping jaws 3′ to reach a certain predetermined position in the slanted hole, arresting section 2′a comes close to gripping jaws 3′ in the rotating direction and prevents nut 2′ from further rotating in the loosening direction.
Chinese patent No. 99101282.8 (Publication No. CN1097503C) discloses a chuck with a jaw stop apparatus. As shown in FIG. 50, the chuck includes a rotating lock gear installed between the nut 2′ and the jaws 3′. When the jaws 3′ reach a predetermined position in the slanted hole, the nut 2′ is prevented from further rotating in the loosening direction. The rotating lock gear includes a radial extending surface 2′a of the limited nut thread end, and the radial surface comes into contact with the lateral surface 3′a of a jaw 3.